This invention relates generally to solenoid control systems and to a cusp detector for use therein. More particularly, this invention relates to a solenoid control system wherein the duration of energization of the solenoid is a function of the workload imposed thereon such that the solenoid is always turned off or the current reduced as soon as the solenoid armature or plunger is seated.
The prior art is replete with examples of electromechanical systems employing electrical solenoids and solenoid control systems. Many printer systems employ solenoid-actuated print hammers; record card feeding devices employ solenoid-operated pickers; and card or check sorters employ solenoid-operated pocket gates.
Many of the solenoid control systems of the prior art have de-energized the solenoid in one or more of the following ways. Most of the systems of the prior art operate to turn off the solenoid at a fixed time after the solenoid is initially turned on. Other types of systems employ mechanical feedback such as relatively slow reacting mechanical switches which sense when the solenoid is seated and operate to de-energize the coil. Still other systems employ photo-optical devices or the like to sense the actual position of the solenoid plunger so as to de-energize the coil when the plunger reaches a predetermined physical position. A few of the systems of the prior art utilize comparison means which determine when a predetermined threshold level of current is reached after the solenoid has seated and then de-energize the solenoid coil.
All of the above-cited systems of the prior art suffer from one or more of the following disadvantages. None of these systems turn off the solenoid at substantially the exact time at which the solenoid seats, resulting in wasted energy since the solenoid continues to be driven after the plunger or armature has seated. This results in greatly increasing the power supply requirements of the system and in the possible generation of excess heat which can damage the solenoid coil or associated circuitry. In addition, the heat which is generated after the plunger has seated, in addition to wasting energy and possibly harming the coil, also reduces the effectiveness of the solenoid by increasing its resistance. Still another disadvantage of many of the systems of the prior art results from the fact that the exact position of the solenoid plunger with respect to the time of the turnoff can vary thereby making it exceedingly difficult to control the damping of the solenoid so as to achieve repeatable damping characteristics. The problem of wasted energy is particularly important in situations in which power supply requirements are critical.